The present invention generally relates to apparatus and methods for extending a spine reconstruction rod and, more specifically, to an apparatus and method for providing a strong, durable inline extension of a spine reconstruction rod.
Referring to FIG. 1, modern reconstructive spine surgery often involves a construct 10 of pedicle screws 12 (only one is shown in the Figure) and a rod 14. FIG. 1 shows a last pedicle screw 12 at an end 16 of the rod 14. One of the major problems with these constructs 10 is that patients will often develop adjacent level disease. It is currently unknown if adjacent level disease is caused by the surgical construct or the result of natural progression of the original condition. It may be a combination of the two causes.
Either way, the adjacent level disease will often make it necessary for the patient to come back later and extend the original construct (e.g., construct 10) up or down the spine. A problem with this extension procedure is how to lengthen the rod to incorporate the new spine levels in the construct. Current methods consist of a “domino” type linkage between the old and new rods.
There are two styles of “domino” linkages. One style is side by side; the other is inline. Both styles are essentially solid blocks of metal. In the side by side, the domino clamps the new rod along the side of the old rod. For the inline configuration, one end of the old rod is slid into the domino while the new rod is slid into the other end of the domino.
A problem with the inline design is that there is not enough space to put the rod of the original construct and the rod of the new construct end to end without having an extended length of spine reconstruction rod (including the length of the domino) that is not attached to the spine with a pedicle screw. In other words, the location where a pedicle screw of the new construct would typically be attached to the spine has to be changed to a location further down (relative to the joint between the new rod and the old rod) the spine due to the domino occupying the space where the first pedicle screw of the new construct would otherwise be located.
Another problem with the inline design is that often there is not enough of a length 16a of rod left on the original construct past the last pedicle screw 26 at the end 16 of rod 14 to insert into the domino.
A problem with the side by side domino design is one of space. The new rod, being placed along side of the original rod, is no longer inline with the original rod. Typically, a rod extension should be inline with the original rod. Therefore, significant bending of the new rod is necessary to bring the new rod back inline with the original rod. This offset and bending makes the final construct weaker than if a single, longer rod were installed according to prior art methods. Such an installation of a single, longer rod, however, as discussed below, requires exposing the entire original rod for its removal. Furthermore, the additional bulk of the side by side construct is also a problem (especially in young, thin children with scoliosis).
Another conventional way to address adjacent level disease is to completely expose the original construct (often involving a very large incision when only a single level needs to be added), remove the old rod, and replace it with a longer rod to immobilize both the original and the new spine reconstruction regions.
As can be seen, there is a need for an apparatus and method for extending a reconstruction rod which does not involve skipping a pedicle screw in the new construct, exposing the entire old construct, or adding a significant amount of size to the junction between the old and new construct.